Question

I am attempting to lean linq by replacing existing code in a project with linq calls. In this method I check for a condition in my list of lines and if the condition is true, move that element from lines to processedLines.

The data structures are just lists:

List<LineSegment2> lines;
List<LineSegment2> processedLines;

The original code was:

for (int i = lines.Count - 1; i >= 0; i--)
{           
   if (lines[i].P2.x < sweepPosition)
   {
      processedLines.Add(lines[i]);
      lines.RemoveAt(i);
   }
}

and my linq code is:

var toMove = lines.FindAll(x => x.P2.x < sweepPosition);
toMove.ForEach(x =>
{
   processedLines.Add(x);
   lines.Remove(x);
});

My question is: Is this linq code less efficient because it is using more memory creating the temporary list ‘toMove’. Is there a way to create the linq query without requiring the temporary list or is the original code always more efficient?

Answer 1

A more LINQy solution would be to add all the processed lines at once, then get the remaining lines:

processedLines.AddRange(lines.Where(x => x.P2.x < sweepPosition));
lines = lines.Where(x => x.P2.x >= sweepPosition).ToList();

As for efficiency, it won’t be quite as fast as your original code. That’s not why you use LINQ.

There is one potential advantage, though. It will make a new list of lines, so if you move a lot of lines to the processed list it will get rid of the unused items in the list.